The long-term objectives of the proposed study are 1) to identify and characterize mouse sperm proteins ("fertilization proteins") which mediate interaction between sperm and egg at the level of the zona pellucida and 2) to determine, at the molecular level, how sperm "fertilization proteins" interact with their counterparts in the zona pellucida. Future studies will focus on identification of analogous human sperm proteins. Identification and characterization of these proteins will undoubtedly lead to specific clinical methods for perturbing fertilization and for detecting and, perhaps, bypassing defects in fertilization. The first specific aim of the proposed study is the identification of the ZP3 recognition protein: i.e., the sperm lectin-like surface protein responsible for primary binding of mouse sperm to the zona pellucida. In primary sperm-egg recognition, the plasma membrane overlying the sperm head binds to ZP3, one of three zona pellucida glycoproteins, at the surface of the zona pellucida. A specific "receptor oligosaccharide" of ZP3 is responsible for the receptor activity of ZP3. A 56,000 dalton (56 KD) mouse sperm surface protein has been identified which has a number of properties expected for the sperm's ZP3 recognition protein. Experiments proposed here are designed to determine whether or not the 56 KD sperm protein plays the in vivo role of ZP3 recognition protein in the mouse. Specifically, this protein will be tested for its affinity for ZP3 and the receptor oligosaccharide of ZP3, using affinity chromatography and affinity blotting techniques. The protein will also be tested for its ability, in soluble form, to block primary sperm-egg binding, using in vitro fertilization techniques. The second specific aim of the proposed study is to determine whether the 56 KD sperm protein is related to other candidate ZP3 recognition proteins. It has been proposed by others that either a sperm galactosyl transferase or acrosin function as the sperm protein which recognizes ZP3. These proteins will be tested for identity with the 56 KD sperm protein on the basis of amino acid sequence and immunological cross-reactivity and, individually, for properties expected of the ZP3 recognition protein.